1. Field of the Invention
The present invention relates to a method for improving a procedure for a wireless communications system and related communications device, and more particularly to a method for improving a MIMO procedure for a network terminal and a UE of a wireless communications system and related communications device.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the 3rd Generation Partnership Project (3GPP) provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency so as to improve uplink/downlink transmission rate.
To further increase the downlink data rate, 3GPP introduces a Multi-input Multi-output (MIMO) technology, with which a user equipment (UE) and a base station, known as a Node-B, utilize multiple antennas to transmit/receive radio signals. Besides, the MIMO technology can be further incorporated with spatial multiplexing, beam forming and spatial diversity technologies to reduce signal interference and increase channel capacity. In the prior art, the MIMO operation is mainly employed to the HSDPA system, doubling the peak rate of high speed downlink share channel (HS-DSCH). Concerning radio resource control (RRC) states of the UE, the MIMO operation is only applicable for the UE in CELL_DCH state.
To control MIMO operation of the UE, a universal terrestrial radio access network (UTRAN) can set configuration of MIMO operation in RRC messages with information elements (IEs) and send the RRC messages to the UE through corresponding RRC procedures. According to an RRC protocol specification of 3GPP, a MIMO parameter IE includes a MIMO operation IE, a MIMO N/M Ratio IE and a MIMO Pilot Configuration IE. The MIMO N/M Ratio IE includes information about the antenna numbers of the UE and the Node-B. The MIMO Pilot Configuration IE includes information about diversity, channelization code, etc. The MIMO operation IE is utilized to indicate the UE to activate, continue or stop the MIMO operation, and correspondingly includes three possible parameter values, which represent “start”, “continue” and “stop”, respectively.
The UTRAN can use an ACTIVE SET UPDATE, CELL UPDATE CONFIRM, or any reconfiguration message to include the MIMO parameter IE and then sends these messages to the UE. On the other hand, the UE contains a MIMO_STATUS variable to store the MIMO configuration data included in the MIMO parameter IE, i.e. parameter values corresponding to MIMO N/M ratio and MIMO pilot configuration.
When the UE receives any aforementioned RRC message, the UE clears the MIMO_STATUS variable if no MIMO parameter IE is included in the RRC message. If the MIMO parameter IE is included in the RRC message and the MIMO operation IE is set to “stop”, the UE clears the MIMO_STATUS variable as well and further triggers lower layers to stop any operation about MIMO. If the UE is notified that the MIMO operation IE is set to “start”, the UE stores the received parameter values in the MIMO_STATUS variable, and then triggers lower layers to start MIMO operation if all corresponding parameters are set. If the MIMO operation IE is set to “continue”, the UE just stores the received parameter values in the MIMO_STATUS variable.
From the above, the prior art specification defines two ways for the UTRAN to stop the MIMO operation of the UE. One way is not including the MIMO parameter IE in the RRC message; the other is setting the MIMO operation IE to “stop”. In the practice of the former way, the UTRAN requires no information bits; in the practice of the latter way, as the above, the MIMO operation IE requires two information bits for three parameter values related to the “stop”, “continue” and “stop” operations. Thus, the latter way results in transmission of extra bits in the RRC messages for MIMO configuration.